Internal combustion engines with carburetors are still in use to a large extent in general aviation (Part 25). The propellers of the aircraft are coupled to the engines directly or with the aid of a nonadjustable gear. In this aircraft class, propellers are predominantly used for the drive, and each has a (hydraulic) propeller speed controller that is controlled via a pull cable and/or via a separate propeller control unit.
Very small deviations among the rotational speeds of the aircraft propellers result in acoustical and vibrational disturbances of the aircraft.
A conventional rotational speed controller is not appropriate, since during the flight operation, uniform running of the engine/propeller is not to be expected on account of external interferences (turbulences). Thus far, for eliminating the rotational speed deviation in multiple engines, the propellers have been synchronized with the aid of a separate controller, and also with the aid of special propeller speed controllers.
The synchronization of the rotational speed of the engines is necessary primarily due to acoustic beats that arise at different engine speeds.